Frost Blankets: Which Weight Do You Need?
A frost blanket — or floating row cover — is spunbonded polypropylene that drapes over plants and traps ground heat, keeping the air underneath several degrees warmer than the open air outside.
It's how growers start earlier in spring, stretch the harvest later into fall, and carry plants through winter. The choice comes down to one number: fabric weight in ounces.
Weight does two things at once: the heavier the fabric, the more frost it holds off — but the less light passes through. So the right blanket is the lightest one that still covers your coldest expected night. Here's how the four weights line up.
Seed germination, seedling establishment, and season extension. Light enough to leave on continuously in spring and fall.
The popular all-rounder for vegetables, row crops, flowering annuals, and bedding plants through spring and fall.
Hard freezes and established shrubs, perennials, and ornamentals through fall and early winter.
Full-winter overwintering for trees, dormant perennials, and extreme cold — leave it in place all season.
How a Frost Blanket Works
During the day the ground absorbs heat; at night a frost blanket traps that radiant warmth before it escapes, holding a microclimate under the fabric several degrees above the outside air. Because the fabric is spunbonded rather than solid plastic, water and air pass straight through — so plants stay hydrated and don't cook, and you can leave the cover on for days or weeks at a time. It's light enough to drape directly over a bed (that's the “floating” in floating row cover), or you can run it over hoops to keep it off tender new growth.
Light vs. Warmth: The Trade-Off
This is the whole decision in one sentence: more warmth means less light. The lighter weights (0.5–1 oz) pass roughly 75–90% of available light, so they're made to stay on actively growing crops for the long haul — the plants keep photosynthesizing right through the cover. The heavier weights (1.5–2.5 oz) block more frost but only let 30–50% of light through, which is exactly what you want for dormant shrubs, perennials, and trees in deep winter, but too dark to leave over plants you're trying to grow. The move is to pick the lightest weight that still covers your coldest expected night, not the heaviest one you can buy.
Commercial-Grade, Not Box-Store
All four weights are professional-grade spunbonded polypropylene in commercial roll sizes — from narrow 6′ strips up to 50′ field covers — with seams that are sewn, not glued, so they hold up season after season instead of pulling apart the first windy night. That durability is the real difference from the thin, fused covers sold at big-box stores, and it's why commercial growers and nurseries buy by weight and roll size rather than by the pre-cut package.
Pick the Lightest Weight That Covers Your Cold
Reaching for a heavier blanket than you need just steals light and slows growth; going too light leaves plants exposed on the one night that matters. Start from your lowest expected temperature and whether the plants are actively growing or dormant, then choose the lightest weight that clears that low — that's the blanket that protects without holding your crop back.
Quick Selection Checklist
- 1. Start with weight: 0.5 oz (2–4°F), 1 oz (4–6°F), 1.5 oz (6–8°F), 2.5 oz (8–10°F) of protection
- 2. Actively growing crops? Stay light (0.5–1 oz) so ~75–90% of light still gets through and you can leave it on for weeks
- 3. Dormant winter protection for shrubs, perennials, or trees? Go heavy (1.5–2.5 oz) and accept the lower light
- 4. Match the weight to your coldest expected night, then pick the lightest one that covers it
- 5. Every weight breathes — water and air pass through — so plants stay hydrated under cover
Popular places to start: 0.5 oz for germination and season extension, 1 oz as the all-purpose row cover for vegetables, 1.5 oz for hard freezes and shrubs, and 2.5 oz for full-winter overwintering — all in commercial roll sizes with sewn seams and free shipping.
Not sure which weight fits? Use the Frost Blanket Selector above — tell it what you're protecting and how cold it gets, and it points you to the right weight.
